This section provides background information related to the present disclosure which is not necessarily prior art.
Conventional, hermetically-sealed, electric power terminal feed-throughs (also referred to as “hermetic terminals”) serve to provide an airtight electrical terminal for use in conjunction with hermetically sealed devices, such as air conditioning (A/C) compressors. In such applications, maintaining a hermetic seal is a critical requirement, and leakage through the hermetic terminal must be effectively precluded. FIG. 1 shows a schematic illustration of an A/C compressor 100 in which is installed a hermetic terminal 200 which enables electric power to be carried to a motor located within a sealed housing. The hermetic terminal is constructed to prevent the compressed, pressurized refrigerant gas 102 from escaping through the terminal 100.
An exemplary conventional hermetic terminal 200 that is well-known in the art is shown in FIG. 2. In such conventional hermetic terminals 200, an electrically conductive pin 202 is fixed in place within an aperture or opening 204 through a metal terminal body 206 by an electrically insulating fusible sealing glass 208 that forms a hermetic, glass-to-metal seal between the pin 202 and the terminal body 206. Optionally, a ceramic insulating sleeve 210 surrounds each pin 202 on the interior side of the terminal body 206 and is secured in place by the sealing glass 208. Additionally, a resilient electrical insulator 212 can optionally be bonded to the outside surface of the terminal body 206, as well as over the glass-to-metal seal 208 and portions of the current-conducting pins 202.
In a conventional hermetic terminal 200, the terminal body 206 is typically manufactured from cold rolled steel in a stamping operation that forms the cap-like shape of the terminal body 206, as well as the openings 204 through the top wall 214 of the terminal body. As a result of the stamping, the openings 204 through the top wall 214 of the terminal body 206 are formed to create a lip portion 216 that serves as a surface against which the fusible sealing glass 208 can create the hermetic seal. The surface area created by the lip portion 216, which has a length extending about two times or more the thickness of the top wall 214 of the terminal body 206, ensures that a sufficient seal can be made to achieve a desired hermeticity.
In addition to hermeticity, burst pressure is a critical performance specification for hermetic terminals, particularly those used in high-pressure applications. The performance requirements for high-pressure hermetic terminals often demand that the hermetic terminals be capable of maintaining hermeticity at pressures more than 20 MPa (i.e., several thousand pounds per square inch). In high-pressure air conditioning compressors, for example, hermetic terminals can be required to meet burst pressure ratings of 33 MPa (about 4800 psi). Any deformation of the terminal body under high pressure can compromise the integrity of the hermetic seal and result in failure of the hermetic terminal. Consequently, it is generally accepted that high-pressure hermetic terminals require a more robust (i.e., thicker) terminal body.
The dimensions of the hermetic terminal in combination with limitations in stamping technology, however, limit the maximum thickness of a terminal body that can be produced by a metal stamping process to only about 3.5 millimeters. Moreover, as the thickness of the material forming the terminal body increases toward 3.5 millimeters, the ability to form the lip portion in the opening (which provides the surface where hermetic seal can be made) during the stamping operation diminishes. Metal stamping has, therefore, been found to be unsuitable for forming a terminal body for a high-pressure hermetic terminal.
In order to achieve the necessary combination of hermeticity and burst pressure performance in high-pressure applications, then, high-pressure hermetic terminals generally incorporate a thicker terminal body. One exemplary high-pressure hermetic terminal 300 is illustrated in FIG. 3. As shown, the top wall 314 of the terminal body 306 is substantially thicker t2 than the thickness t1 of the top wall 206 of the conventional hermetic terminal 200 of FIG. 2, at least in part because of the need to provide adequate surface area for forming a sufficient hermetic seal. For example, a terminal body 306 having a top wall thickness t2 of about 6 millimeters has been found to demonstrate the necessary strength under high pressure, while providing the surface area needed to enable the sealing glass 308 to form an adequate hermetic seal with the terminal body 306. The thicker terminal body 306, however, cannot readily be manufactured in a cost-effective manufacturing operation such as metal stamping. Instead, the thicker terminal bodies 306 are generally fabricated in the more costly manufacturing process of machining from bar stock. In addition, the bar stock from which the terminal bodies 306 are machined can include defects in the form of inclusions that can run vertically through the thickness t2 of the top wall 314 of the machined terminal body 306. The inclusions can, in turn, lead to defects that increase the scrap rates of the machined parts.
Consequently, there remains a need for an improved high-pressure hermetic terminal that can meet the necessary combination of hermeticity and burst pressure performance in high-pressure applications and can be manufactured efficiently in a high-volume production environment, such as by stamping.
The present disclosure provides a hermetic power terminal feed-through for use in high-pressure applications. The hermetic power terminal can include a fused pin subassembly comprising a tubular reinforcing member and a current-conducting pin. The current-conducting pin passes through the tubular reinforcing member and can be fixed thereto by a fusible sealing material to create a hermetic seal. The fused pin subassembly can then be permanently joined and hermetically sealed to a terminal body by brazing or soldering.
The construction of the hermetic terminal of the present disclosure enables the terminal body to be made from a metal material that is thinner than the metal material conventionally employed in high-pressure hermetic terminals. Notwithstanding the thinner terminal body, the hermetic seal provided and the strength of the terminal body satisfy the performance demands of a high-pressure operating environment. The reduced thickness of the terminal body makes it suitable for forming in the economical manufacturing process of metal stamping.
Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.